Method for rolling steel sheet and method for manufacturing steel sheet

Abstract

Provided is a method for rolling a steel sheet and a method for manufacturing a steel sheet capable of preventing occurrence of defects in appearance of a steel sheet caused by oil spots of a coolant and preventing occurrence of defects in shape of a steel sheet by appropriately controlling thermal deformation of work rolls. The method for rolling a steel sheet according to the present invention is a method for rolling a steel sheet involving feeding of a coolant to rolls that form a rolling mill during the rolling. The method includes keeping a coolant feeding rate at or lower than a predetermined rate lower than an upper constant rate at a start of operation of the rolling mill, and increasing the coolant feeding rate to the upper constant rate in response to an amount of center buckles of the steel sheet reaching or exceeding an upper target value.

The invention claimed is: 
     
       1. A method for rolling a steel sheet including feeding a coolant to rolls that form a rolling mill during the rolling, the method comprising:
 keeping a coolant feeding rate at or lower than a predetermined rate lower than an upper constant rate at a start of operation of the rolling mill; and 
 increasing the coolant feeding rate to the upper constant rate when an amount of center buckles of the steel sheet reaching or exceeding an upper target value, 
 wherein a profile steepness of the steel sheet at a center portion is used as the amount of center buckles, the profile steepness being calculated by dividing a height difference value in a wave cycle in a sheet thickness direction at the center portion of the steel sheet by a wavelength, and 
 wherein the center portion is an area extending from a widthwise center line to both sides in a width direction within a range of 5% of a width of the steel sheet. 
 
     
     
       2. The method for rolling a steel sheet according to  claim 1 , wherein the coolant feeding rate is decreased from the upper constant rate to a lower constant rate when the amount of center buckles of the steel sheet reaching or falling below a lower target value. 
     
     
       3. The method for rolling a steel sheet according to  claim 2 , wherein the rolling is a secondary cold rolling performed after an annealing. 
     
     
       4. A method for manufacturing a steel sheet, comprising performing surface treatment after performing the rolling with the method for rolling a steel sheet according to  claim 3 . 
     
     
       5. The method for rolling a steel sheet according to  claim 1 , wherein the rolling is a secondary cold rolling performed after an annealing. 
     
     
       6. A method for manufacturing a steel sheet, comprising performing surface treatment after performing the rolling with the method for rolling a steel sheet according to  claim 5 .